Plants require the element nitrogen for growth. Plants obtain nitrogen by absorbing it from the soil through their roots. A variety of nitrogen-containing compounds are commonly added to the soil as fertilizers to improve plant growth.
Corn is the most important crop grown in the United States. Corn is also known as maize and has the scientific name Zea mays. Corn has a growing season of about four to six months. Corn requires a relatively large amount of nitrogen, especially in the period of about twenty to eighty days after germination.
Nitrogen is commonly added to corn fields in the form of anhydrous (water free) ammonia, the chemical symbol of which is NH3. The use of ammonia fertilizer is the least expensive way of adding a desired quantity of nitrogen to a corn field. Ammonia is a gas at atmospheric pressure and ambient temperatures, but is typically stored and transported in the liquid phase in pressurized containers. The liquid ammonia changes to gas upon release into atmospheric pressure.
Ammonia is generally applied to a corn field by dragging a wheeled ammonia tank and a wheeled applicator (commonly known as a toolbar) behind a tractor. Attached to the toolbar are a number of knives that create parallel trenches (also known as furrows) in the field. Supply lines run from the ammonia tank to outlets at the bottom of each knife. Ammonia is discharged into the bottom of each trench and the trench is then immediately filled by the action of disc sealers, two of which trail behind each knife. The dirt pushed back into the trench prevents excessive amounts of ammonia gas from escaping before it can dissolve in the water present in the soil.
Ammonia is added to corn fields at various times during the growing season. It is sometimes added before planting, but nitrogen levels decrease over time. Therefore, to achieve a desired level of nitrogen in the soil during the critical period of corn plant growth, application during the critical period requires the least amount of ammonia. The corn plants are typically a few inches tall at the beginning of the critical period. When ammonia is added at this time, it is applied to the space between adjacent rows of corn plants. Application of ammonia when the corn plants are growing is commonly known as “side dressing.”
One disadvantage of side dressing is that the young corn plants are easily damaged. Damage can occur both directly and indirectly. If the ammonia toolbar is not dragged precisely through field (i.e., so that the knives, wheels, and/or trailing disc sealers travel in the space between the rows of corn plants), the knives, wheels, and/or trailing disc sealers can directly damage the plants. The second, indirect way damage occurs is by the action of dirt particles that are thrown upward and outward as the knives pierce the soil. The term “dirt particles” is used herein to refer to dirt particles of all sizes. To reduce the damage, ammonia application equipment is typically pulled through the fields at a relatively low speed. The low speed reduces the area that can be fertilized in a given amount of time and increases the cost.
A variety of horizontal shields that are attached to plows and knives have been disclosed. Some shields are designed and intended to travel along the surface. For example, Harryman, U.S. Pat. No. 970,818, Sep. 20, 1910, discloses a plow with an attached horizontal shield. The shield is dragged along the surface of the ground to control the depth at which the plow extends into the ground. As another example, Bruce, U.S. Pat. No. 5,452,673, Sep. 26, 1995, discloses an ammonia knife with a trailing attached plate. The plate drags along behind the knife and closes the trench, thereby replacing the conventional disc sealers. The Harryman shield is not suitable for use with wet soil because a build-up of material occurs. The Bruce shield has no effect on the dirt particles that are thrown upward and outward from the leading edge of the knife.
Other horizontal shields are designed and intended to travel below the surface. Brannan, U.S. Pat. No. 3,605,657, Sep. 20, 1971, discloses an ammonia knife having two angled moldboards that are below ground level during use. The purpose of the moldboards is to direct dirt onto the applied ammonia and to immediately provide a seal. Thompson et al., U.S. Pat. No. 5,520,125, May 28, 1996, discloses an earthworking sweep that follows a chemical applicator. The sweep is below ground level during use and is intended to direct dirt onto the applied chemical. Dietrich, Sr., U.S. Pat. No. 6,397,767, Jun. 4, 2002, discloses a liquid fertilizer knife having horizontal wedge members. The wedge members are below ground level during use and are intended to direct dirt onto the applied fertilizer. The Brannan, Thompson et al., and Dietrich, Sr. horizontal members have no effect on the dirt particles that are thrown upward and outward from the leading edges of the knives.
Accordingly, a demand exists for a side dressing shield for an ammonia knife that prevents thrown dirt particles from damaging adjacent corn plants. A demand also exists for a method of side dressing corn that reduces the indirect damage to the corn plants caused by thrown dirt particles.